Method of preparing lead article

ABSTRACT

A solid rigid lead article having improved resistance to creep and comprising a consolidated blended admixture of particulate lead or lead alloy, and, from about 0.5 to 15 percent by volume of solid particulate non-metallic material so intimately and thoroughly dispersed and embedded throughout the article that inter-particle distances between non-metallic particles are substantially not greater than about 10 microns and preferably are less than about 1 micron. The solid particulate material is further characterized as being finer than about 200 mesh, as being solid-insoluble in lead, as having a melting temperature above about 622*F and as being substantially free from gaseous decomposition or evolution below about 622*F. A method of preparing the article also is disclosed.

United States Patent Foerster 1 Sept. 26, 1972 [54] METHOD OF PREPARING LEAD 3,416,918 12/1968 Roberts .75/206 ARTICLE 3,179,515 4/1965 Grant et al ..'....75/206 2 inventor: George S. Foerster Midland Mich. 3,377,143 4/1968 Alexander ..75/206 X 4-8640 Primary Examiner-Allen B. Curtis [73] Assignee: Dow Chemical Company, Mid- Attorney-Griswold and Burdick, Edward E. Schilling land, Mich. and C. Kenneth Bjork [22] Filed; Feb. 6, 1970 [57] ABSTRACT [21] Appl 9397 A solid rigid lead article having improved resistance to Related Application Data creep and comprising a consolidated blended admix- 1 ture of particulate lead or lead alloy, and, from about 0f 672,715. 1967. 0.5 to 15 percent by volume of solid particulate nonabandoncdmetallic material so intimately and thoroughly dispersed and embedded throughout the article that 1 6 75/206 inter-particle distances between non-metallic particles [51] Int. Cl. ..B22f 3/20 are substantially not greater than aboutlO microns [58] Field of Search ..29/ l9ll9l.6; and preferably are less than about 1 micron. The solid 264/ 1 ll particulate material is further characterized as being finer than about 200 mesh, as being solid-insoluble in [56] References Cited lead, as having a melting temperature above about 622F and as being substantially free from gaseous UNITED STATES PATENTS V decomposition or evolutionbelow about 622F. A 2,994,109 8/1961 Thomas ..264/1 11 method of Preparing the article also is disclosed- 3,1s9,9s9 6/1965 Ebdon ..75/206 x 3,294,530 12/1966 Storchheim ..7s/206 x 2 Chums Drawmgs METHOD OF PREPARING LEAD ARTICLE CROSS-REFERENCE TO RELATED APPLICATION This is a division of application Ser. No. 672,715, filed Oct. 4, 1967 now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a lead article prepared from particulate lead and particulate non-metallic material.

For the purposes of the specification and the claims, the term lead metal is understood to include lead and lead-base alloys containing at least about 50 percent by weight-of lead.

2. Description of the Prior Art Although lead is a relatively inert metal, its uses are somewhat limited because of the low strength properties and slight resistance to creep exhibited both by elemental lead itself and to quite an extend by alloys of lead as well. Attempts have been made to improve the resistance to creep of lead by mixing particulate nonmetallic material with particulate lead and ram extruding the mixture. In order to obtain improvement, extremely fine lead powder must be used,.e.g., particles less than about 1 micro in diameter. Extremely fine lead powder is more expensive to produce than ordinary lead powder, i.e., from about 20 to about 200 mesh (U.S. Sieve Series), and is hazardous to handle because of its toxicity.

OBJECT OF THE INVENTION It is a principal object of the invention to provide an improved lead article which exhibits desirable strength properties in addition to improved resistance to creep under load. A further object of the invention is to provide a method of making such improved lead article without requiring the use of ultra-tine lead powder.

SUMMARY OF THE INVENTION The invention is a solid rigid lead metal article and method of its preparation which comprises a consolidated intimate admixture of from about 0.5 to percent by volume, but more preferably 1.5 to 10 percent by volume, of a solid particulate non-metallic material and the balance substantially a particulate lead metal, the solid particulate non-metallic material being so intimately and thoroughly dispersed and embedded throughout the article that inter-particle distances between non-metallic particles are substantially not greater than about l0 microns and preferably are less than about one micron, sometimes averaging about 0.25 micron. The solid particulate non-metallic material is further characterized as having an average particle size small enough to pass about a No. 200 sieve (U.S. Sieve Series), as being solid-insoluble in lead, as having a melting temperature above about 622F. (327C), and as being substantially free from gaseous decomposition or evolution below about 622F. This consolidated composition exhibits improved resistance to creep as compared to screw extruded powdered lead or lead alloy.

The present method is carried out by mixing particulate lead metal with extremely fine or friable nonmetallic, usually inorganic, material and screw extruding the mixture.

, 2' BRIEF DESCRIPTION OF THE INVENTION The lead employed in making the article of the invention is employed in particulate form, tag, as chips,

shavings or atomized pellets having, preferably, average particlesizes passing about a No. 20 to about a No. 325 sieve (U. S. Sieve Series). Smaller particle sizes in this range are preferred to assure maximum dispersion of non-metallic material in the finished article. The particulate lead metal may be prepared mechanically if desired, but is readily prepared by a jet atomizing process in which the molten metal is broken up with a jet of gas such as air or natural gas, or by a wheel atomizing process in which the molten metal-is allowed to fall onto a rapidly spinning disc orwheel.

The'lead may be a commercial grade of lead or one Q of the alloys thereof. Typical lead alloys contain one or more of lead-soluble metal additions including antimony, arsenic, bismuth, calcium, magnesium, silver, tin and mixtures thereof. Generally the lead alloy contains at least about 50 percent by weight of lead.

The solid particulate non-metallic material is selected from materials which are solid-insoluble in lead and which do not melt, vaporize or decompose with gas evolution at temperatures below about the melting point of lead, viz., 622F. (327C.). Particularly suitable solid non-metallic materials include mainly inorganic compounds, such as, oxides of any of lead, magnesium, aluminum or thorium or mixtures thereof. The solid non-metallic material should be either extremely fine or friable enough to break into extremely fine particles during admixing or extrusion. In any case the material should be fine enough to permit uniform coating of the lead particles. The solid nonmetallic material should be fine enough to pass a No. 200 sieve, but preferably is fine enough to pass about a No. 325 sieve (U. S. Sieve Series). It is even more preferable to employ solid particulate non-metallic material having substantially all the particles thereof finer than about one micron in major diameter.

In preparing the article of the invention, the particulate lead metal and the solid particulate non-metallic material in the proportions selected are thoroughly admixed, as in a tumbling container such as a ball mill, until the individual lead metal particles are substantially coated with particles of inorganic material. If desired, the uniformity of coating may be improved by using a small amount of relatively volatile solvent to enhance the spreading of the solid inorganic material over the surfaces of the particles of lead metal. An example of a suitable solvent is ethylene glycol. Such solvent may be employed in an amount in the range of about I to 3 percent by weight of the total charge to be mixed. If desired the lead powder may be coated with an inorganic compound according to the invention on reacting the powder with a suitable liquid or gaseous reagent prior to extrusion. For example, PbO may be formed by heating lead particles in air. Or an inorganic compound may be formed by decomposing a gas on the lead particles. Suitable methods of coating, including chemical deposition, aqueous precipitation, gas plating, and vapor plating which are coating methods well known in the art.

The thoroughly mixed charge of metal and inorganic material is then placed, for example, in the hopper of a screw extruder, such as the continuous screw extrusion press described in U. S. Pat. No. 2,787,022. The charge of the admixture may be pre-heated, if desired, to a temperature of about 300F. In any event the press itself is operated at a temperature of about 300F. During screw extrusion the mixture of particulate material is further mixed and the particle structure is broken down due to the combination of longitudinal and transverse working of the mixture as it is expressed through a die opening by the action of the screw on the powder mixture.

The extrusion reduction ratio (the cross-section of the extruded section) is preferably between 10:1 and 100:1 although ratios as high as 200:1 or as low as 2:1

may be used. The extruded product obtained is the solid rigid article of the invention.

EXAMPLES The following examples are illustrative of the invention.

Lead ingot of commercial purity was melted and jet atomized by exposing a thin stream of the molten metal to a jet of natural gas so that the molten metal was dispersed into fine, substantially spherical droplets that solidified in the surrounding ambient atmosphere. The particles of atomized lead had sizes predominantly in the range of 20 to 200 mesh (U. S. Sieve Series). Two different powder mixtures were made up by admixing pre-selected portions of magnesium oxide powder with the particulate lead. The magnesium oxide powder was very fine; substantially all the particles passing a No. 200 sieve. The two mixtures made up contained, respectively by weight, 0.5 and 2.5 percent of magnesium oxide. The magnesium oxide employed is sufficient to provide, in the consolidated products, respectively, approximately 1.5 and 7.4 percent by volume of magnesium oxide.

The powder mixtures were placed, at respective times, in a metal container having a volume of about 2 gallons and the mixtures were tumbled by rotating the container on its axis for about l5 minutes in each case. The thoroughly mixed powder mixtures were each in turn placed in the hopper of a screw extrusion press maintained at a temperature of about 300F. and screw extruded into one-eighth inch by 1 %inch strip at a reduction ratio of about 20:1. The so-obtained extruded strip was subjected to physical testing to determine per cent elongation, tensile yield strength, ultimate tensile strength and resistance to creep. The results of the tests are summarized in Table 1.

In an additional test carried out by way of comparison, a quantity of the jet atomized pellets of lead which had not been admixed with magnesium oxide powder was screw extruded into strip in the same manner as the powder mixtures. Samples of the extruded strip were likewise subjected to physical testing and the results also are summarized in Table I.

In yet an additional comparison test an ingot of commercial grade lead was extruded into strip in a ram extrusion press under similar conditions of temperature and reduction ratio. The results of physical testing of this strip also are summarized in the table.

TABLE 1 I: Creep I Creep Rate Material Physical Properties In 100 extension Run No. Extruded k8 TYS TS Hours per year 2 Pb+2 3-4 2.6-4.4 2.7-5.2 .030 1.3 Compa- Pb Powder 34-38 1.8 2.8-2.9 .054 3 risonl Compa- Pb lngot 57 2.6 ca. 35

In a manner similar to the foregoing, mixtures of par- 7 ticulate commercial grade lead and lead base alloys containing antimony, arsenic, bismuth, calcium, magnesium, silver and tin with from 0.5 to percent by volume of any of finely powdered MgO, PbO, PbO

A1 0 and Th0, are screw extruded to provide the solid rigid lead article of the invention which exhibits desirable creep resistance properties.

The preferred article of the invention contains from 0.5 to 3 percent by weight of finely divided magnesium oxide and the balance commercial grade lead or leadbase alloy.

The method and article of the invention having been thus fully described, various modifications thereof will at once be apparent to those skilled in the art and the scope of the invention is to be considered limited only by the breadth of the claims hereafter appended.

1 claim:

1. The method of making a solid rigid article of lead metal which comprises wetting particulate lead with about 1 to 3 percent by weight of volatile solvent,

blending the particulate lead metal with from about 0.5

to a screw-extrusion operation whereby the blend is consolidated into a rigid article, the reduction ratio during the screw-extrusion operating being a ratio in the range of about :1 to 10:1 and each of the blended material and the extrusion press being at a temperature of about 300 F. the solid particulate nonmetallic material being further characterized (l) as having an average particle size small enough to pass about a No. 200 sieve (U.S. Sieve Series), (2) as being solid-insoluble in lead, (3) as having a melting temperature above about 622 F. (327C), and (4) as being substantially free from gaseous decomposition below about 622 F.

2. The method of making a solid rigid article of lead metal which comprises blending particulate lead metal with from about 0.5 to 15 percent by volume of solid particulate non-metallic material based on the weight of the blended mixture, and thereafter subjecting the blended material to a screw-extrusion operation whereby the blend is consolidated into a rigid article, the reduction ratio during the screw extrusion operation being a ratio in the range ofabout 100:1 to 10:1 and each of the blended material and the extrusion press employed being at a temperature of about 300 F., the solid particulate non-metallic material being further characterized (l) as having an average particle size small enough to pass about a No. 200 sieve U.S. Sieve Series), (2) as being solid-insoluble in lead, (3) as having a melting temperature above about 622 F.

(327 C.), and (4) as being substantially free from gaseous decomposition below about 622 F.

Patent No.

Inventor(s) CERTIFICATE OF CORRECTION Georqe Foerster It is certified that error appears'in the above-ddentifimi patent and that said Letters Patent are hereby corrected as shown below:

Column 4 (Table I) under the column heading 1311 N o add "rison 2" on line 6;

under the column heading Material Extruded,

as. part of the entry for Run No. 1, add

"MgO" after "Pb 0. 5%"

under the column heading Material Extruded as part of the entry for Run No. 2,

add "MgO" after Pb 2. 5.

(SEAL) Attest:

EDWARD M. FLETCHER,JR.

ROBERT GOTTSCHALK Attestlng Officer Commissioner of Patents CERTIFICATE OF CQRRECTIQN Patent No. 3 694, 536 D t d September 26, 1972 ln nt fls) Georqe Foerster It is certified that error appears'in the above-identified patent and that: said Letters Patent are hereby corrected as shown below:

Column 4 (Table I) under the column heading Bun N o add "rison 2" on line 6;

under the column heading Material Extruded,

under the column heading Material Extruded as part of the entry for Run No. 2,

add "Mg O" after Pb 2.5.

Signed and sealed this 6th day "6f March'l973.

1 (SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attestlng Officer Commissioner of Patents 

2. The method of making a solid rigid article of lead metal which comprises blending particulate lead metal with from about 0.5 to 15 percent by volume of solid particulate non-metallic material based on the weight of the blended mixture, and thereafter subjecting the blended material to a screw-extrusion operation whereby the blend is consolidated into a rigid article, the reduction ratio during the screw extrusion operation being a ratio in the range of about 100:1 to 10:1 and each of the blended material and the extrusion press employed being at a temperature of about 300* F., the solid particulate non-metallic material being further characterized (1) as having an average particle size small enough to pass about a No. 200 sieve U.S. Sieve Series), (2) as being solid-insoluble in lead, (3) as having a melting temperature above about 622* F. (327* C.), and (4) as being substantially free from gaseous decomposition below about 622* F. 